Conveying device for open-cast mines

ABSTRACT

A conveyor for opencast installations, is described, the conveyor includes at least one conveyor belt driven by at least one drive, or a device resembling a conveyor belt. Overburden or raw materials such as coal, for example, is extracted by an extracting unit and transported further by the conveyor belt.

FIELD OF THE INVENTION

The present invention relates to a conveyor for opencast installations,having at least one conveyor belt driven by at least one drive, or adevice resembling a conveyor belt, overburden or raw materials such ascoal, for example, being extracted by means of an extracting unit andtransported further by means of the conveyor belt.

BACKGROUND INFORMATION

In opencast installations, raw materials such as coal, for example, arefrequently transported many kilometres on conveyor belts or devicesresembling conveyor belts. A great deal of electric energy is consumedin this transporation.

SUMMARY

It is therefore an object of the present invention to promote a conveyorfor opencast installations in which the energy consumption can besubstantially lowered by comparison with known conveyors for opencastinstallations as described in, for example, German Patent No. 42 40 094.In addition, it is particularly desirable to reduce the maintenanceoutlay for conveyors.

According to the present invention, a conveyor is provided in which thetorque/time curve of the conveyor device is monitored so that:

rapid changes in torque are detected;

the changes in the torque are detected for purposes of detecting slidingslippage (unloading of the device) or as blockage.

Whereas conventional conveyors for opencast installations are runcontinuously at one speed, which essentially corresponds to a speedrequired for maximum conveying power, according to the presentinvention, the speed is matched to the slippage, particularly in thecase of starting up, as a result of which the demand for electric energyis also reduced.

When sliding slippage is identified according to the present invention,the driven torque may be adapted, in the short term, for example, bysuperimposed regulation of the available power transmission (frictionangle, Eytelwein equation). In this way, slippage in the belt drives maybe prevented to a great extent. Additionally, the drives may transmitthe available torque (friction angle, satisfaction of the Eytelweinequation) in a force-closed fashion under all operating conditions(e.g., dynamic changes in belt tension, starting up slippage, snow,rain, wear and, thus, different drum diameters on the same system). Thetorques of the individual drives for the multiple drive system of a beltinstallation may be corrected, leading to a better utilization of thedrives and to a reduction in wear.

In one example embodiment of the present invention, the controller orthe regulator sets the speed of the conveyor belt in such a way that theconveyor belt is fully utilized. This operating point corresponds to amaximum energy savings. Since the running power is reduced inconjunction with the same rate of conveyance, an increase in servicelife is provided, and the maintenance outlay is reduced.

In a further example embodiment of the invention, the conveyor systemhas a monitoring device which is designed to monitor the conveyor belt,in particular with temporal foresight, for overload and to preventoverloading of the conveyor belt. In this way, overloading of theconveyor belt is avoided by the increase in speed according to thepresent invention. The monitoring with foresight, which renders itpossible for the conveyor belt to be accelerated in good time despiteits high inertia, allows the system to react to peak loads withreference to the overburden to be transported or to the raw materials.

In an example embodiment of the present invention, the speed of theconveyor belt is determined by the maximum value of the overburden orraw material to be transported in a specific time interval. Largecontrol movements in the drives and possible overloading due to theinertia of the conveyor belt are prevented in this way. In this case,the time interval is advantageously longer than the time for running theconveyor belt up to maximum speed.

In a further example embodiment of the present invention, the conveyorhas at least one measuring device by means of which the quantity of theoverburden to be transported or of the raw materials to be transportedis measured. The measurement may be carried out so early thatdiscontinuities with respect to the quantity of overburden or rawmaterials to be transported are detected in such good time that theconveyor belt can be accelerated to a speed which corresponds to the newload state.

In order to prevent costly damage to the conveyor, controllers orregulator and/or the measuring device may be designed to be at leastdoubly redundant, the values they supply being compared with oneanother. If, given two-fold redundancy, said values deviate from oneanother, the conveyor belt is accelerated to its maximum speed. Givenmultiple redundancy, the faulty component can be identified andeliminated.

In a further example embodiment of the present invention, the conveyorhas variable-speed drives, in particular variable-speed three-phase ACmotors.

The energy saved by the conveyor according to the present invention isyielded as follows: Saving of energy loss W per startup in rotorresistances, liquid or eddy-current couplings of conventional drives inthe case of runup with the slipage control: $\begin{matrix}{W = \frac{0.5\quad P_{N}f\quad t_{A}}{3600}} & (1)\end{matrix}$

Here, P_(N) is the nominal power of the motors in kW, f being thestarting load factor, that is to say the mean starting torque, and t_(A)being the runup time in seconds. The equivalent power loss P_(vz) duringthe operating time T_(B) is calculated as follows: $\begin{matrix}{P_{VZ} = \frac{Z_{a}W}{T_{B}}} & (2)\end{matrix}$

Here, Z_(a) is the number of startups per year. According to equations(1) and (2), $\begin{matrix}{\frac{P_{VZ}}{P_{N}} = \frac{0.5\quad {fZ}_{a}t_{A}}{3600\quad T_{B}}} & (3)\end{matrix}$

for the power loss referred to the nominal power P_(N).

Taking account of the required power P_(B) and of the load factor, itholds for the saving on power loss P_(VD) caused by the repeatedslippage S_(D) without motor slippage that: $\begin{matrix}{\frac{P_{VD}}{P_{N}} = {\eta_{L}{kS}_{D}}} & (4)\end{matrix}$

In this case, h_(L) is the load factor, i.e., the mean conveying powerQ_(M) referred to the nominal conveying power Q_(N), and k is therequired power P_(N), in the case of nominal conveying power referred tothe nominal power P_(N), that is to say K=P_(B)/P_(N). The result is asaving in friction power and churning power by matching the belt speed Vto the conveyance discharge Q in accordance with the followingcalculations:

The friction power and churning power at a constant belt speed V_(N),i.e., for V=V_(N)=const., is: $\begin{matrix}{\frac{Q}{Q_{N}} = \frac{m}{m_{N}}} & (5)\end{matrix}$

Here, Q is the conveyance discharge, m the mass of the material to beconveyed on the conveyor belt and M_(N) the mass of the material to beconveyed on the conveyor belt in the case of nominal loading. It holdsin general for the friction power that P_(R)=F_(R) V. Using equation(5), it holds for V=V_(N)=const. that: $\begin{matrix}{\frac{P_{R}}{P_{RN}} = {\frac{F_{R}}{F_{RN}} = {f\left( \frac{Q}{Q_{N}} \right)}}} & (6)\end{matrix}$

Here, P_(RN) is the friction power or churning power in the case ofnominal conveying power, F_(R) is the friction force and churning force,and F_(RN) is the nominal friction force and churning force. Thefunction can be described in an approximate fashion in accordance with(6) by the following formula: $\begin{matrix}{\frac{P_{R}}{P_{RN}} = {\lambda_{V} + {\left( {1 - \lambda_{V}} \right)\frac{Q}{Q_{N}}}}} & (7)\end{matrix}$

a value for l_(v) of between 0.3 and 0.6, in particular a value ofl_(v)=0.53 having proved through measurements to be particularlysuitable.

It holds for the friction power and churning power in the case of const.loading m_(N) for m=m_(N)=const. that: $\begin{matrix}{\frac{Q}{Q_{N}} = \frac{V}{V_{N}}} & (8)\end{matrix}$

it holding with P_(R)=F_(R) V that: $\begin{matrix}{\frac{P_{R}}{P_{RN}} = {\frac{F_{R}}{F_{RN}}\frac{V}{V_{N}}}} & (9)\end{matrix}$

The function F_(R)=f(v) can be represented to a first approximation bythe following formula. With equation (8) it holds that: $\begin{matrix}{\frac{F_{R}}{F_{RN}} = {\lambda_{m} + {\left( {1 - \lambda_{m}} \right)\frac{Q}{Q_{N}}}}} & (10)\end{matrix}$

a value of around l_(m)=0.79 having proved through measurement to beparticularly suitable.

According to equations (9) and (10), it holds for the friction power andchurning power that: $\begin{matrix}{\frac{P_{R}}{P_{RN}} = {{\lambda_{m}\frac{Q}{Q_{N}}} + {\left( {1 - \lambda_{m}} \right)\left( \frac{Q}{Q_{N}} \right)^{2}}}} & (11)\end{matrix}$

The saving DP_(R) on friction power and churning power as a function ofthe conveying power is yielded from the difference between equations (7)and (11). $\begin{matrix}{\frac{\Delta \quad P_{R}}{P_{RN}} = {\lambda_{V} + {\left( {1 - \lambda_{V} - \lambda_{m}} \right)\frac{Q}{Q_{N}}} - {\left( {1 - \lambda_{m}} \right)\left( \frac{Q}{Q_{N}} \right)^{2}}}} & (12)\end{matrix}$

the saved friction power and churning power referred to the nominalpower of the motors is yielded [lacuna] $\begin{matrix}{\frac{\Delta \quad P_{R}}{P_{N}} = {f\left( \frac{Q}{Q_{N}} \right)}} & (13)\end{matrix}$

The following equation holds for the required power P_(B) of the drivemotors:

P_(B)=P_(HN)+P_(RN)=K P_(N)  (14)

Here, P_(HN) is the nominal lifting power in the case of nominalconveying power Q_(N), that is to say P_(HN)=g·H·Q_(N), g being theacceleration of free fall and H the height of lift.

According to P_(RN) equation (14) yields: $\begin{matrix}{P_{RN} = {{KP}_{N}\left( {1 - \frac{P_{HN}}{{KP}_{N}}} \right)}} & (15)\end{matrix}$

When substituted in equation (12), equation (15) yields: $\begin{matrix}{\frac{\Delta \quad P_{R}}{P_{N}} = {{K\left( {1 - \frac{P_{HN}}{{KP}_{N}}} \right)}\left\lbrack {\lambda_{V} + {\left( {1 - \lambda_{V} - \lambda_{m}} \right)\frac{Q}{Q_{N}}} - {\left( {1 - \lambda_{m}} \right)\left( \frac{Q}{Q_{N}} \right)^{2}}} \right\rbrack}} & (16)\end{matrix}$

The saved power is yielded from the arithmetic mean value of equation(16) during the operating time t_(B). $\begin{matrix}{\frac{\Delta \quad P_{Rm}}{P_{N}} = {\frac{1}{T_{B}}{\int_{0}^{T_{B}}{\frac{\Delta \quad P_{R}(t)}{P_{N}}{t}}}}} & (17)\end{matrix}$

To a first approximation, the mean value DP_(RM) can be determined bysubstituting the mean conveying power Q_(m)=h_(L) Q_(N) in equation(16). It therefore holds for the saved energy that: $\begin{matrix}{\frac{\Delta \quad P_{Rm}}{P_{N}} \approx {{K\left( {1 - \frac{P_{HN}}{{KP}_{N}}} \right)}\left\lbrack {\lambda_{V} + {\left( {1 - \lambda_{V} - \lambda_{m}} \right)\eta_{\lambda}} - {\left( {1 - \lambda_{m}} \right)\eta_{L}^{2}}} \right\rbrack}} & (18)\end{matrix}$

Accordingly, an energy saving of up to 17% is yielded for an averagerate of conveyance h_(L)=0.75.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment for the use of a conveyor accordingto the present invention.

FIG. 2 shows the principle of the mode of operation of a belt weigheroperating in a contactless fashion.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment for the use of a conveyor accordingto the present invention. In this case, raw materials, in particularcoal, are extracted by extracting units 7, 8, 9, 10, for exampleexcavators, and passed to a conveyor belt 1. The raw materials aretransported to a loading device 5 by means of the conveyor belt 1 andfurther conveyor belts 2, 3, 4. In the exemplary design, the conveyorbelt 1 is operated at a speed which is required to remove the rawmaterials when the extracting units 7, 8, 9, 10 are operating at maximumoutput. The conveying power is determined by means of a measuringdevice, which is designed, in particular, in a redundant fashion. Theconveyor belts 2, 3 and 4 then have their speeds matched to the massflow in conjunction with an appropriate time delay. For example, if theconveying unit 7 is initially not in operation and is then taken intooperation during operation of the extracting units 8, 9, 10, the resulton the conveyor belt 1 is an increase in the conveying power, that is tosay the filled height in the conveyor belt 1 rises given a constantspeed of the conveyor belt. This rise is detected in the measuringdevice 6, and the conveyor belts 2, 3 and 4 are accelerated. Themeasuring device 6 can be, for example, a belt weigher, or a beltweigher operating in a contactless fashion in accordance with FIG. 2.

FIG. 2 shows the principle of the mode of operation of a belt weigher,operating in a contactless fashion, for measuring the mass flow or theconveyed mass of a bulk material 21, i.e., raw materials or overburden,on a conveyor belt 20. The belt weigher according to the presentinvention has a filled height measuring device 22 and a densitymeasuring device. The density measuring device has a radiation source 24and a radiation receiver 25. The radiation 26 emitted by the radiationsource 24 and received by the radiation receiver 25 penetrates theconveyor belt 20 and bulk material 21. For evaluation purposes, thefilled height measuring device 22 and the density measuring device areconnected to an evaluation unit 23. However, evaluation can also beperformed in the density measuring device or in the filled heightmeasuring device 22. The data connection between the density measuringdevice, filled height measuring device and evaluation unit 23 can beperformed via a bus system or point-to-point connections.

What is claimed is:
 1. A conveyor for opencast installations,comprising: at least one extracting unit extracting one of overburdenand raw materials; a conveyor belt transporting the one of theoverburden and the raw materials; a drive driving the conveyor belt, atime derivative of a torque of the drive being monitored for exceeding apredetermined tolerance value; and a controller setting a speed of theconveyor belt as a function of a quantity of the one of the overburdenand the raw materials to be transported.
 2. The conveyor according toclaim 1, wherein the one of the overburden and the raw material is coal.3. The conveyor according to claim 1, wherein the controller sets thespeed of the conveyor belt so that the conveyor belt is fully utilized.4. The conveyor according to claim 1, further comprising: a monitormonitoring the conveyor belt, the monitor predictively monitoring theconveyor belt for overload.
 5. The conveyor according to claim 4,wherein a time interval for predicting overload is longer than a timefor running the conveyor belt up to maximum speed.
 6. The conveyoraccording to claim 1, further comprising: at least one measuring devicemeasuring the quantity of the overburden and the raw materials to betransported.
 7. The conveyor according to claim 6, wherein the at leastone measuring device determines the quantity of the one of theoverburden and the raw materials to be transported before the one of theoverburden and the raw materials reaches the conveyor belt.
 8. Theconveyor according to claim 4, wherein the monitor is at least doublyredundant.
 9. The conveyor according to claim 6, wherein the at leastone measuring device is at least doubly redundant.
 10. The conveyoraccording to claim 1, wherein a slippage between the conveyor belt andthe drive is determined as a function of a time derivative of the torqueof the drive.
 11. The conveyor according to claim 10, furthercomprising: a slippage controller correcting the slippage between theconveyor belt and the drive as a function of time derivative.